Unit For Generating and Treating Compressed Aeriform Fluids, With an Improved Cooling System

ABSTRACT

The unit ( 1 ) comprises
         a positive-displacement compressor ( 2 ) including:   a prime mover ( 4 ),   a rotatable shaft ( 5 ) rotatable by the prime mover ( 4 ), and   at least one cylinder ( 7 - 10 ) in which an associated piston ( 11, 12 ), coupled to the shaft ( 5 ) by means of a crank mechanism ( 13, 14 ), is mounted for sliding in a leaktight manner; and   a heat-exchanger unit ( 3 ) for receiving and cooling the compressed fluid produced by the compressor ( 2 ).       

     The unit comprises at least one tapping duct ( 41; 41   a,    41   b ) extending between the heat-exchanger unit ( 3 ) and that region of the at least one cylinder ( 7 - 10 ) which is disposed between the associated piston and the shaft ( 5 ), the duct being suitable for supplying a flow of compressed fluid to that region in operation in a manner such that the flow of fluid can expand and be cooled further in that region.

The present invention relates to a unit for generating and treating acompressed aeriform fluid, in particular air.

More specifically, the subject of the invention is a generating andtreatment unit comprising

-   -   a positive-displacement compressor including    -   a prime mover,    -   a rotary shaft rotatable by the prime mover, and    -   at least one cylinder in which an associated piston, coupled to        the shaft by means of a crank mechanism, is mounted for sliding        in a leaktight manner; and    -   a heat exchanger for receiving and cooling the compressed fluid        produced by the compressor.

The object of the present invention is to provide a generating andtreatment unit of the type specified above which comprises in particulara so-called “oil-free” positive-displacement compressor, that is, apositive-displacement compressor without lubrication, which has animproved cooling system that can afford the compressor a long operativelife.

This and other objects are achieved according to the invention by a unitof the type defined above, characterized in that it further comprises atapping duct extending between the heat exchanger and that region of theat least one cylinder which is disposed between the associated pistonand the shaft, the duct being suitable for supplying a flow ofcompressed fluid to that region in operation in a manner such that theflow of fluid can expand and be cooled further in that region.

By virtue of this characteristic, an efficacious cooling effect isproduced on the rotational bearings of the crank mechanism by means ofwhich the or each piston is connected to the rotary shaft. This coolingis particularly important in oil-free compressors, that is, compressorswithout forced or splash lubrication. In fact, as is known, slidingbearings which are intended to operate without forced lubrication areprovided with thin films of solid lubricant or with sealed bearingunits, which are susceptible to failure at temperatures above about 70°C. Control of their operative temperature is therefore essential for along useful life of these bearings.

Further characteristics and advantages of the invention will becomeclear from the following detailed description which is given purely byway of non-limiting example with reference to the appended drawings, inwhich:

FIG. 1 is a perspective view of a unit for generating and treating airaccording to the present invention;

FIG. 2 is another perspective view of the unit shown in FIG. 1;

FIG. 3 is a perspective view similar to that shown in FIG. 1 and showsthe generating and treatment unit without the cooling fans associatedwith its cylinders;

FIG. 4 is a perspective view showing part of FIG. 3 on an enlargedscale; and

FIGS. 5 and 6 are sections taken on lines V-V and VI-VI of FIG. 3,respectively.

In FIGS. 1 to 3, a unit for generating and treating a compressedaeriform fluid, in particular air, according to the invention isgenerally indicated 1.

In the embodiment shown, the unit 1 comprises a positive-displacementcompressor, generally indicated 2 in FIG. 3, and an associatedheat-exchanger unit, generally indicated 3 in FIG. 2 et seq.

The heat-exchanger unit 3 comprises, for example, two exchange sections,each of which is of the type with parallel vanes through which a bundleof tubes arranged in parallel with one another, or a coil, extends.

In the embodiment shown, the positive-displacement compressor 2comprises a prime mover 4 (FIGS. 1-3), for example an electric motor,which rotates a crankshaft 5 in operation (FIGS. 3-6). The crankshaft 5is mounted for rotation in a substantially box-shaped rigid supportcasing 6 connected to the housing of the prime mover 4.

In the embodiment shown by way of example, the positive-displacementcompressor 2 comprises two pairs of cylinders 7, 8 and 9, 10, arrangedin opposed pairs (a “boxer” arrangement). However, the invention is notlimited to this number of cylinders or to their arrangement at 180°.

The cylinders 7-10 are connected to the support structure 6 and anassociated piston is mounted for sliding in a leaktight manner in eachcylinder. Only the pistons 11 and 12 which are mounted for sliding inthe cylinders 9 and 10 are visible in the appended drawings (FIG. 5).

The above-mentioned pistons are coupled to the crankshaft 5 in knownmanner by means of respective crank mechanisms including connecting rods13 and pins 14 for articulation between the connecting rods and thepistons (FIG. 5).

With reference to FIGS. 3 and 4, the cylinders 7, 9 and 8, 10,respectively, that are situated on the same side of the supportstructure 6 have respective intake connectors connected to correspondingintake manifolds 15 and 16. The cylinders have respective output ordelivery ducts connected to corresponding portions of the heat-exchangerunit 3. The heat exchanger is intended to cool the compressed fluidwhich is output by the compressor 2 and is destined for a user pneumaticcircuit, not shown.

The intake manifolds 15 and 16 are connected to a support plate 17(FIGS. 1-3) interposed between the support structure 6 and the housingof the prime mover 4.

A fan unit, generally indicated 18 in FIGS. 1 and 5, is associated withthe positive-displacement compressor 2. In the embodiment shown by wayof example, the fan unit 18 comprises a support structure 19 which issubstantially C-shaped in cross-section (FIG. 5) with an upper arm orlimb 20, a lower arm or limb 21 and a shaped intermediate portion 22 inwhich four openings 27-30 are defined, facing the cylinders 7-10,respectively. Respective electric fans 37-40 for producing an air-flowfor cooling the associated cylinders of the compressor 2 are mounted inthe openings (FIGS. 1, 5 and 6).

The motor-driven fans 37-40 are preferably of the “suction” type withrespect to the associated cylinders 7-10 although the possibility oftheir being of the “pusher” type is not excluded.

As can be seen in particular from FIGS. 1, 2 and 5, the end arms 20 and21 of the support structure 19 are joined to the opposite ends of thetwo sections of the heat exchanger 3 and, together with the transverseplate 17 and with an end plate 31 (FIG. 2) facing the transverse plate17, help to define a compact, substantially parallelepipedal box-likecasing enclosing the support structure 6 of the crankshaft 5 and thecylinders 7-10 of the positive-displacement compressor.

With reference to FIGS. 3, 4 and 6, in the generating and treatment unit1 according to the invention, a respective tapping duct is associatedwith the cylinders of the compressor which extend from the same side ofthe central support structure 6. In FIGS. 3, 4 and 6, solely the tappingduct 41 associated with the cylinders 8 and 10 is visible. Withparticular reference to FIG. 6, the tapping duct 41 extends from theassociated section of the heat exchanger 3, outside and above thesupport structure 6, and then extends into that structure through anopening indicated 42 (FIGS. 4 and 6). In the embodiment shown, thetapping duct 41 splits inside the support structure 6 forming twobranches 41 a and 41 b (FIGS. 3 and 4) which are bent into an L-shapetowards the associated pistons. The terminal ends of the branches 41 aand 41 b of the tapping duct 41 extend in those regions of the cylinders8 and 10 which are disposed between the associated pistons and thestructure 6 in which the crankshaft 5 is supported for rotation.

As an alternative to the arrangement described above, the tapping duct41 could extend from a point downstream of a drying device (known)connected to the output of the heat exchanger 3 or from a drain regionof such a drying device.

In operation, a flow of compressed and cooled air is withdrawn from theend portion of the heat exchanger 3 through the tapping duct 41 and itsterminal branches 41 a and 41 b and is fed into the region underlyingthe pistons in the cylinders 8 and 10. The flow of compressed and cooledair expands in that region and brings about effective cooling of thepistons, of the associated articulation pins 14, and of thecorresponding connecting rods 13. This cooling effect prevents thetemperature of the bearings of the crank mechanisms from increasing inoperation so as to avoid the risk of damage to the lubricant filmsassociated with those bearings, ensuring a corresponding extension oftheir useful life.

The pistons and the cylinders are also effectively cooled.

Although it is not visible in the drawings, a similar tapping duct isalso provided for the cylinders 7 and 9 of the other bank.

An electronic control unit, housed, for example, in a holder 50connected to the casing of the prime mover 4, is advantageouslyassociated with the motor-driven fans 37-40, (FIGS. 1 and 3).

The control unit is advantageously arranged to activate the motor-drivenfans 37-40 with a predetermined advance with respect to the starting ofthe prime mover 4 and to de-activate the motor-driven fans with apredetermined delay after the de-activation of the prime mover.

The extent of the advance in the activation of the motor-driven fans isadvantageously predetermined according to the temperature detected inoperation at one or more points in the unit, for example, in thevicinity of a cylinder head or in the vicinity of a crank mechanism. Thesame advantageously applies to the delay in the de-activation of themotor-driven fans.

The delayed switching-off of the motor-driven fans prevents or at leastreduces the thermal shocks borne by the cylinders of thepositive-displacement compressor.

Naturally, the principle of the invention remaining the same, the formsof embodiment and details of construction may be varied widely withrespect to those described and illustrated purely by way of non-limitingexample, without thereby departing from the scope of the invention asdefined in the appended claims.

In embodiments not illustrated, a plurality of motor-driven fans isassociated with the or each cylinder.

In other embodiments not shown a single motor-driven fan is associatedwith two or more cylinders.

In any case, the speed of rotation of the motor-driven fan or fans canadvantageously be controlled in a manner such as to prevent theformation of ice on the heat exchanger or exchangers 3.

In any case, the or each motor-driven fan and/or the respective controlcan be such that the direction of rotation of the motor-driven fan orfans is reversible according to the outside temperature and/or thetemperature of the aeriform fluid at the output of the heat exchanger 3.In this case, it is possible to arrange for switching of the directionof rotation according to the external climatic conditions.

This enables heated air withdrawn from the region surrounding thecylinder head or heads to be sent towards the heat exchanger, forexample, in certain ambient climatic conditions. This is useful inparticular when the exchanger is associated with a membrane dryer whichbecomes inefficient at low temperatures of the air circulating therein,in particular below 0°.

In embodiments comprising membrane dryers the speed of rotation of themotor-driven fan or fans can advantageously be controlled in accordancewith a predetermined function of the external temperature and/or of thetemperature of the aeriform fluid at the output of the heat-exchangerunit 3 to take account, for example, of the fact that the dryersgenerally operate inefficiently at temperatures below about 0° C.

Finally, although the foregoing description and the appended drawingsrelate to a single-stage positive-displacement compressor, the inventionis of course also applicable to multi-stage compressors.

1. A unit (1) for generating and treating a compressed aeriform fluid,in particular air, comprising a positive-displacement compressor (2)including a prime mover (4), a rotatable shaft (5) rotatable by theprime mover (4), and at least one cylinder (7-10) in which an associatedpiston (11, 12), coupled to the shaft (5) by means of a crank mechanism(13, 14), is mounted for sliding in a leaktight manner; and aheat-exchanger unit (3) for receiving and cooling the compressed fluidproduced by the compressor (2), the generating and treatment unit beingcharacterized in that it comprises at least one tapping duct (41; 41 a,41 b) extending between the heat-exchanger unit (3) and that region ofthe at least one cylinder (7-10) which is disposed between theassociated piston and the shaft (5), the duct being suitable forsupplying a flow of compressed fluid to that region in operation in amanner such that the flow of fluid can expand and be cooled further inthat region.
 2. A unit according to claim 1 which is associated with adryer connected to the output of the heat-exchanger (3) and in which theat least one tapping duct (41) extends from a point downstream of theoutput of the dryer.
 3. A unit according to claim 1 in which anelectrically-controlled, motor-driven fan (37-40) is associated with theat least one cylinder (7-10).
 4. A unit according to claim 3 in whichcontrol means (50) are associated with the or each motor-driven fan(37-40) and can bring about the de-activation thereof with apredetermined delay with respect to the de-activation of the prime mover(4).
 5. A unit according to claim 3 in which control means (50) areassociated with the or each motor-driven fan (37-40) and are arranged tobring about the activation thereof with a predetermined advance withrespect to the activation of the prime mover (4).
 6. A unit according toany one of claim 3 in which the extent of the advance and/or delay ispredetermined in dependence on a temperature detected in the unit.
 7. Aunit according to claim 6 in which the temperature is detected in thehead of the at least one cylinder.
 8. A unit according to claim 6 inwhich the temperature is detected in the crank mechanism (13, 14).
 9. Aunit according to any one of claim 3 in which the at least onemotor-driven fan (37-40) and/or associated control means can bring abouta reversal of the direction of rotation of the at least one motor-drivenfan (37-40), and hence a reversal of the ventilation air-flow, accordingto the outside temperature.
 10. A unit according to claim 1, comprisinga single cylinder in which an associated piston is mounted for slidingand with which at least one motor-driven fan is associated.
 11. A unitaccording to claim 1 comprising a plurality of cylinders (7-10) in whichrespective pistons (11, 12) are mounted for sliding in a leaktightmanner, at least one respective motor-driven fan (37-40) beingassociated with each cylinder (7-10).
 12. A unit according to claim 11in which a respective plurality of motor-driven fans is associated witheach cylinder (7-10).
 13. A unit according to claim 1 comprising aplurality of cylinders (7-10) in which respective pistons (11, 12) aremounted for sliding in a leaktight manner, a motor-driven fan beingassociated with two or more of the cylinders.
 14. A unit according toclaim 11 in which the or each motor-driven fan is driven at a speed ofrotation such that the formation of ice on the heat-exchanger (3) isprevented.
 15. A unit according to claim 11 with which at least onemembrane dryer is associated, and in which the or each motor-driven fanis driven at a speed of rotation which varies in accordance with apredetermined function of the external temperature.
 16. A unit accordingto claim 1 in which the or each motor-driven fan (37-40) is driven at aspeed an in a direction of rotation which are determined in accordancewith predetermined procedures according to the temperature of theaeriform fluid at the output of the heat-exchanger unit (3).
 17. A unitfor generating and treating a compressed aeriform fluid, in particularair, substantially as described and illustrated and for the purposesspecified.